Set in the year 2020, the series followed the adventures of the Terrahawks, a taskforce responsible for protecting Earth from invasion by a group of extraterrestrial androids and aliens led by Zelda. Like Anderson's previous puppet series, futuristic vehicles and technology featured prominently in each episode.

It's 1999 and Moonbase Alpha has been built on the Moon to safeguard the nuclear waste shipped from Earth. On September 13, 1999, disaster strikes and the nuclear waste explodes causing a chain reaction that hurls the Moon out of Earth's orbit and into deep space. The adventures of Space:1999 begin.

Around 1970, the British and American governments receive incontrovertible evidence that aliens exist and are abducting humans. In cooperation with the United Nations, they set up a secret worldwide organization, SHADO (Supreme Headquarters Alien Defence Organisation), which operates in the 1980s. With resources and equipment under the seas, in the air, on land, in orbit and on the Moon, SHADO's purpose is to stop the alien incursions and find out why the aliens want humans.